In Scene 4, after Cauchon describes the threat Joan poses to the Church, Warwick lays out the feudal lords' case against her. He uses a metaphor to explain the "nominal" power of the king and the real power of the feudal lords, but his explanation contains situational irony:
Nominally we hold our lands and dignities from the king, because there must be a keystone to the arch of human society; but we hold our lands in our own hands, and defend them with our own swords and those of our own tenants.
Warwick compares the king to "a keystone to the arch of human society." A keystone lies at the top of a stone arch. Wedge-shaped, it snuggles between the rest of the stones and locks them into place so that the arch won't fall. Calling something a keystone usually emphasizes its importance, but Warwick uses the metaphor a bit differently. He admits that the king holds human society together because someone has to. Still, he suggests that the king's power to distribute land is more "nominal" than anything—it is for show, so no one gets upset and demands to know why feudal lords have land while the tenants who work for them do not. He claims that "we [the feudal lords] hold our lands in our own hands." The metaphor of the king as the keystone in the arch of human society slides into the idea that the feudal lords hold up the whole world and do not need the keystone except for show.
It is ironic, though, that he insists on the feudal lords' self-sufficiency given the rest of his sentence. He claims that "we defend [our lands] with our own swords and those of our own tenants." Warwick thinks of the tenants and their swords as an extension of his property. To Shaw's audience in the 1920s, this is obviously not the case. It is not that the lords are defending their land with their tenants' swords, but rather that the tenants are defending their lords' property with no thanks except for their continued ability to live there. Lords build their wealth, and tenants put their lives on the line. It is ironic that Warwick thinks he and the other feudal lords don't need any help given that the current system relies heavily on help from the lowborn who are really holding up the arch of society.
Scene 6 depicts Joan's trial. When the inquisitor explains to an indignant Courcelles that he has reduced the charges from sixty-four counts to twelve, he uses verbal irony that at once cushions Courcelles's ego and makes him appear ridiculous to the audience:
Master de Courcelles: I am the culprit. I am overwhelmed with admiration for the zeal displayed in your sixty-four counts; but in accusing a heretic, as in other things, enough is enough. Also you must remember that all the members of the court are not so subtle and profound as you, and that some of your very great learning might appear to them to be very great nonsense. Therefore I have thought it well to have your sixty-four articles cut down to twelve—
If we are to take the Inquisitor at face value, he thinks it is "admirable" that Courcelles has come up with so many counts on which to charge Joan for heresy. He is simply worried that other people in the courtroom are not as smart as Courcelles and will be unable to see the difference between different charges. He is protecting Courcelles from being accused, by other members of the court, of spouting nonsense.
Reading between the lines, the Inquisitor is only pretending to admire Courcelles. In fact, he is insulting him. "Enough is enough," he says. Ultimately, all the charges amount to the same thing: Joan is an accused heretic. They only need so many reasons to burn her. The Inquisitor does not name which members of the court are less "subtle and profound" than Courcelles. What he really seems to mean is that there is no meaningful distinction between a number of the charges Courcelles has drawn up. They are redundant, and Courcelles needs to learn to edit. Suggesting that some unnamed member of the court might mistake the longer charges for nonsense is a backhanded way of saying that they are, in fact, nonsense. The verbal irony in this moment demonstrates a double standard in the Church: Courcelles's "zeal" is more over-the-top even than Joan's zeal for her cause, and yet she is the only one on trial.
In Scene 6, Joan uses verbal irony to respond to Courcelles's accusation that she must be a witch:
COURCELLES. When you were left unchained, did you not try to escape by jumping from a tower sixty feet high? If you cannot fly like a witch, how is it that you are still alive?
JOAN. I suppose because the tower was not so high then. It has grown higher every day since you began asking me questions about it.
Courcelles is embellishing the truth. Joan really did try to escape. He uses this escape attempt against her not as evidence that she is defiant of her punishment but as evidence that she is a witch. After all, he asks her, how else would she have been able to survive a 60-foot jump? She must be able to fly, which would make her a witch. In order to refute this conclusion, Joan tries to answer Courcelles's question. As she always does, she takes what he says at face value. If the tower is 60 feet high, she suggests, it must have grown. In fact, she tells him, the tower has been taller every time he has asked her about it.
Of course, the tower is not actually growing. Instead, Courcelles is reporting it to be taller and taller each time he mentions it. What Joan means implicitly is that Courcelles is lying, but what she says explicitly is that this whole misunderstanding is the tower's fault. This moment of verbal irony is one of several that suggest that Joan might not be so naive as she acts. Her naivety and insistence on engaging in good faith in every argument might be a strategy she cultivates to point out others' shortcomings. If Joan were to say outright that she is not a witch, it would be her word against Courcelles's. Instead, she uses irony to make it clear that he is not the honest and upstanding Christian he pretends to be.
In Scene 6, after Joan's execution, the executioner reports to Warwick that the job is done. He seems to be speaking literally, but his report is tinged with dramatic irony and metaphorical meaning:
THE EXECUTIONER. Her heart would not burn, my lord; but everything that was left is at the bottom of the river. You have heard the last of her.
The executioner means that the physical organ of Joan's heart refused to burn. Although organ tissue is not necessarily the part of the body that is most resistant to burning, it is true that it requires extraordinarily hot fire to completely incinerate a body. Part of the executioner's job, if burning people is a form of execution, is disposing of remnants that have not been reduced to ash. He is simply telling Warwick that he has burned Joan and disposed of the remains in the river. He genuinely believes that Warwick has "heard the last of her."
But anyone reading or watching Shaw's play in the 20th century and beyond knows that Joan will only get more famous after her death. Centuries later, people are still talking about her. The whole reason Shaw was inspired to write Saint Joan is because the Catholic Church canonized her as a saint as recently as 1920. This future knowledge allows the audience to enjoy a sense of dramatic irony at the executioner's assertion that Warwick and the world have heard the last of Joan. On the contrary, her execution has ensured that the world will never stop hearing about her. Additionally, the fact that Joan has been made a saint gives metaphorical meaning to the phrase "Her heart would not burn." Saint Joan represents extraordinary faith and commitment to her cause. Whereas the executioner thinks of her as a mere human woman, the audience knows her as a legend. Her fire-resistant "heart" becomes not just an organ, but her strength of character.
In the Epilogue, Ladvenu tells Charles that Joan has been cleared of all charges. He uses hyperbole and a hint of verbal irony as he reassures Charles that he wasn't crowned by a heretic:
CHARLES. Good. Nobody can challenge my consecration now, can they?
LADVENU. Not Charlemagne nor King David himself was more sacredly crowned.
CHARLES [rising]. Excellent. Think of what that means to me!
Ladvenu compares Charles to two of the most legendary kings. Charlemagne was an emperor who united most of Western Europe for the first time since the Western Roman Empire had fallen to Byzantine rule; Charlemagne was the first Western Roman Emperor in three centuries, and he launched a massive campaign to spread Christianity throughout Europe. King David is an even more significant religious figure. In the Bible, he is most famous for his rags-to-riches ascension after he kills the giant Goliath, proving himself worthier to rule than the neglectful King Saul. Ladvenu is being hyperbolic in his comparison. It would be nearly impossible for anyone to be as "sacredly crowned" as these larger-than-life figures. By invoking them, he reassures Charles that his crown is as safe as safe can be.
But Shaw, if not Ladvenu himself, is being ironic as well as reassuring. Charles VII is not an especially legendary king—this much Shaw and his audience know. Most of his notable successes were in fact Joan of Arc's successes. On its surface, the statement that "Not Charlemagne nor King David himself was more sacredly crowned" means that Charles VII's crowning was as sacred as that of the most important kings in history and mythology. On a deeper level, the line means that none of these kings were sacredly crowned. Or, if they were, to be sacredly crowned does not mean much of anything.
In the Epilogue, after the Church has cleared Joan's name, she and all the men who condemned her appear to Charles VII in a dream. In a twist of situational irony, despite all their praise for Joan in the dream, none of the men want to see her brought back to life:
JOAN. [...] And now tell me: shall I rise from the dead, and come back to you a living woman?
A sudden darkness blots out the walls of the room as they all spring to their feet in consternation. Only the figures and the bed remain visible.
JOAN. What! Must I burn again? Are none of you ready to receive me?
Joan, still as earnest as she was in life, believes what she hears when the men praise her. They have all been speaking about her as though she is Christ himself, suffering for the sake of everyone else. She draws the logical conclusion: because everyone has agreed that she should not have been burned, she will now get a second chance at life, just like Christ. The sudden "consternation" of all the men demonstrates that once again, Joan has missed the reality of the situation. Whereas their newfound reverence for her ought to mean that they want to see her alive again, instead they want credit for praising her without having to cooperate with her again. These men, just like the Church leaders who finally canonized Joan in the 20th century, are hypocrites. They offer Joan too little too late and want it to mean something. Shaw uses this dream sequence in the epilogue to invite his audience to laugh at the irony of honoring someone after they are dead.
